The present invention relates to a semiconductor device and a method for manufacturing the same.
Some semiconductor devices include non-volatile memories. A non-volatile memory is an element which retains stored data even when the power is off. A highly functional semiconductor device can be provided by mounting a non-volatile memory over a semiconductor substrate which is used in a semiconductor device for logical operation. A semiconductor device which includes such a non-volatile memory is widely used as an embedded microcomputer in industrial machines, home electric appliances, in-vehicle devices and so on.
One type of non-volatile memory cell structure is a cell structure which includes two transistors: a transistor for selection and a transistor for memory. This type of cell structure is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2004-200504.
The selection transistor selects a cell of a non-volatile memory. The memory transistor stores data by changing the threshold voltage by charge accumulation. The memory transistor has a MONOS (Metal Oxide Nitride Oxide Semiconductor) structure.
Another type of non-volatile memory cell structure is a structure which has only a memory transistor for charge accumulation.